Evidence for male-mediated developmental toxicity derives from strong animal data and from several epidemiological studies that exposures of fathers to environmental toxicants are associated with adverse consequences to the fetus and offspring. The proposed research will investigate the roles of specific paternal host factors and environmental risk factors for the transmission of chromosomal defects via sperm. Chromosomally defective sperm are detrimental to the developing embryo and live-born child resulting in spontaneous abortions and birth defects. Two promising sperm FISH methods have been recently developed to detect human sperm carrying abnormal numbers of chromosomes (aneuploidy) or structurally defective chromosomes (partial chromosomal duplications, deletions, or breakage). Studies with these sperm methods indicate that chromosomally defective sperm are inducible after exposures to certain drugs, both in murine and human studies; however, the utility of the genetic biomarkers in sperm in the assessment of reproductive hazards in occupationally or environmentally exposed populations remains to be proven. In addition, the modifying effects of host factors are not known. The objectives of the proposed research are to investigate the relationship of age and diet on sperm chromosomal defects in healthy non-smoking men and to determine if occupational exposure to benzene is associated with increases in the proportions of chromosomally defective sperm and with reduced semen quality. The specific aims are to: (a) characterize the relationship between age and chromosomal defects in sperm of approximately 100 healthy men aged approximately 20-80y, contrasting the age-defects on chromosome structure defects in sperm against numerical defects and semen quality; (b) examine the associations between diet and chromosomally abnormal sperm utilizing food- frequency questionnaire and seminal measurements of specific nutrients; and (c) investigate the effects of moderate-to-high occupational exposure to benzene (at or above US permissible levels) on chromosomal defects in sperm and semen quality for a group of approximately 50-benzene- exposed Chinese workers and approximately 40 unexposed controls. We will also compare the semen effects of benzene against its chromosome toxicity to lymphocytes We propose to investigate benzene because it is an important Superfund chemical, a proven human leukemogen, and occupational exposure induces chromosomal damage in lymphocytes. This project will contribute towards understanding male reproductive human health, specifically: (a) the importance of age and diet as paternal risk factors for chromosomally defective sperm, and (b) whether these genetic biomarkers in human sperm can be used as early warning signals for the identification of paternally mediated embryo-toxicity and teratogenicity due to exposure to Superfund chemicals. This project also has the exciting potential of identifying benzene as a human germinal mutagen, which would be extreme importance in assessing health risk to the unborn near Superfund sites.